Electrolyser module

ABSTRACT

Liquid communication means for an electrolyser module comprising a plurality of structural plates each having a sidewall extending between opposite end faces with a half cell chamber opening and at least two degassing chamber openings extending through the structural plate between the opposite end faces, the liquid communication means facilitating liquid communication between the at least two degassing chambers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.13/609,732 filed Sep. 11, 2012, which is a continuation-in-part of U.S.application Ser. No. 12/501,790 filed Jul. 13, 2009, now U.S. Pat. No.8,308,917, issued Nov. 13, 2012, which claims priority to CanadianApplication No. 2637865 filed Jul. 15, 2008. The disclosures of theabove applications and patents are herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to the design of electrolysers for theproduction of gases such as hydrogen and oxygen, or hydrogen andnitrogen, or hydrogen and chlorine, and more particularly, to a waterelectrolyser module and components therefor.

BACKGROUND OF THE INVENTION

Electrolysers use electricity to transform reactant chemicals to desiredproduct chemicals through electrochemical reactions, i.e., reactionsthat occur at electrodes that are in contact with an electrolyte.Hydrogen is a product chemical of increasing demand for use in chemicalprocesses, and also potentially for use in hydrogen vehicles powered byhydrogen fuel cell engines or hydrogen internal combustion engines (orhybrid hydrogen vehicles, also partially powered by batteries).Electrolysers that can produce hydrogen include: water electrolysers,which produce hydrogen and oxygen from water and electricity; ammoniaelectrolysers, which produce hydrogen and nitrogen from ammonia andelectricity; and, chlor-alkali electrolysers, which produce hydrogen,chlorine and caustic solution from brine and electricity.

Water electrolysers are the most common type of electrolyser used toproduce gaseous hydrogen. The most common type of commercial waterelectrolyser currently is the alkaline water electrolyser. Alkalinewater electrolysers utilize an alkaline electrolyte (typically anaqueous solution of, e.g., 25% to 35% KOH) in contact with appropriatelycatalyzed electrodes. Hydrogen is produced at the surfaces of thecathodes (negative electrodes), and oxygen is produced at the surfacesof the anodes (positive electrodes) upon passage of current between theelectrodes. The rates of production of hydrogen and oxygen areproportional to the current flow in the absence of parasitic reactionsand stray currents and for a given physical size of electrolyser. Theelectrolyte solute (potassium hydroxide) is not consumed in thereaction, but its concentration in the electrolyte may vary over a rangewith time, as a result of discontinuous replenishment of water reactedand also lost as water vapour with the product gases.

As used herein, the terms “half cell”, “half electrolysis cell” andequivalent variations thereof refer to a structure comprising oneelectrode and its corresponding half cell chamber that provides spacefor gas-liquid (electrolyte) flow out of the half cell. The term“cathode half cell” refers to a half cell containing a cathode, and theterm “anode half cell” refers to a half cell containing an anode.

As used herein, the terms “cell”, “electrolysis cell” and equivalentvariations thereof refer to a structure comprising a cathode half celland an anode half cell. A cell also includes a separator membrane(referred to herein after as a “membrane”), typically located between,and in close proximity to or in contact with, the cathodes and anodes.The functionality of the membrane is to maintain the hydrogen and oxygengases produced separate and of high purity, while allowing for ionicconduction of electricity between the anode and cathode. A membranetherefore defines one side of each half cell. The other side of eachhalf cell is defined by an electronically conducting solid plate,typically comprised of metal, and generally known as a bipolar plate.The functionality of the bipolar plate is to maintain the fluids inadjacent half cell chambers of adjacent cells separate, while conductingcurrent electronically between adjacent cells. Each half cell chamberalso contains an electronically conducting component generally known asa current collector or current carrier, to conduct current across thehalf cell chamber, between the electrode and the bipolar plate.

Practical (commercial) alkaline water electrolysers utilize a structurecomprising multiple cells, generally referred to as a “cell stack”, inwhich the cells typically are electrically connected in series (althoughdesigns using cells connected in parallel and/or series also are known).A cell stack typically consists of multiple cells, with bipolar platesphysically separating but electrically connecting adjacent cells. Asused herein, the term “structural plate” refers to a body which definesat least one half cell chamber opening and at least two degassingchamber openings. A cell stack typically is constructed using a seriesof structural plates to define degassing chambers, and alternatelycathode and anode half cell chambers for fluid (gas-liquid mixtures andliquid) flow. The structural plates also hold functional components,which may include, for example, cathodes, anodes, separator membranes,current collectors, and bipolar plates, in their appropriate spatialpositions and arrangement. The series of structural plates andfunctional components typically constitutes a filter press typestructure, including end (and in some cases, intermediate) pressureplates. The gases generated at the electrodes form gas-liquid mixtureswith electrolyte in the half cell chambers, which typically arecollected at the exits of the half cell chambers. The gas-liquidmixtures must be treated in degassing chambers, which serve to separatethe respective gases from the entrained electrolyte. The terms“electrolyser module” or “electrolyser” refer to a structure comprisedof an electrolyser cell stack and its associated degassing chambers.

Most practical water electrolyser modules today utilize large steelvessels located above the cell stack as degassing chambers (alsocommonly known as gas-liquid separators). There are two general designapproaches for circulating fluids in an electrolyser module (i.e., forcirculating gas-liquid mixtures from the cell stack to the degassingchambers, and then returning degassed liquid from the degassing chambersto the cell stack).

In the first general design approach, gas-liquid mixtures from eachcathode half cell are collected in a manifold above the half cellchambers in the top part of the cell stack, which is connected to thecorresponding (hydrogen) degassing chamber via a pipe or tube externalto the cell stack; a similar arrangement is used for the anode halfcells and the corresponding (oxygen) degassing chamber. The separatedliquid is returned from the degassing chambers via piping or tubing thatis external to the cell stack to a manifold or manifolds located in thecell stack, beneath the half cell chambers, from which liquidelectrolyte is fed back into the individual cathode half cell chambers.There are two main corresponding practical (commercial) sub-approaches.

In the first sub-approach, exemplified in U.S. Pat. No. 4,758,322, theseparated liquid in the degassing chambers is mechanically pumped backinto the cell stack. While mechanical pumping overcomes the pressuredrops in the horizontal manifolds in the cell stack and the externalpiping or tubing, and allows for large numbers of cells in a singlestack (e.g., 200 or more cells), there are several associateddisadvantages. For example, the use of a pump adds complexity, capitaland operating cost, maintenance requirements, and may adversely affectthe availability of the electrolyser module. The pump generally isoperated at all times during module operation at a liquid flow ratecorresponding to that required for the maximum nominal gas productionrate, resulting in maximum associated power losses. Although a dualmechanical pump electrolyser module configuration also is disclosed,typically in practical (commercial) electrolyser modules, a singlemechanical pump circuit is used to circulate liquid collected from bothdegassing chambers back to both the cathode half cell chambers and anodehalf cell chambers; this maintains equal pressures on either side of themembrane in each cell, but typically adversely affects gas purities byintroducing the other gas (entrained in the returning liquid) into boththe anode and cathode half cell chambers.

In the second sub-approach, exemplified in U.S. Pat. No. 6,554,978, theanode and cathode fluids are kept separate by relying on gas lift[buoyancy] and gravity head to circulate the fluids in separate circuitswithout pumps. Advantages of this design approach are the potential tomaintain high gas purities and inherently self-regulating fluid flows;however, the number of cells per cell stack is limited by the pressuredrop across the horizontal manifolds in the cell stack and the externalpiping or tubing, and the available vertical space to provide pressurehead. Note that the sizes of the manifolds and the conduits connectingthe manifolds to the individual half cells are limited by therequirement to restrict stray currents. Consequently, this particularapproach generally has been limited to relatively small productioncapacities, with an associated requirement to use multiple cell stacksor multiple complete electrolyser modules to reach higher productioncapacities.

In the second general design approach, gas-liquid mixtures from eachhalf cell chamber are fed to the corresponding degassing chamber viagas-liquid feed conduits for each individual half cell chamber. Theseparated liquid is returned from the degassing chamber via externalpiping or tubing to a manifold located beneath the half cell chambers,which feeds liquid electrolyte back into the individual half cellchambers. This approach, while somewhat more scalable in terms of thenumber of cells in a single cell stack, requires a significant amount ofpiping and assembly, with many mechanical connection points, eachrepresenting a potential leak point. Furthermore, scalability remainslimited by pressure drops across the common degassed liquid return path,i.e., the external piping or tubing and manifold beneath the half cellchambers in the bottom portion of the cell stack. Electrolyser modulesusing the second general design approach typically utilize mechanicalpumps to circulate the fluids.

In all of the above approaches, the physical size of the electrolysermodule, i.e., its lack of compactness for any given hydrogen gasproduction capacity, is problematic. In an attempt to obtain a morecompact electrolyser module, developmental designs that incorporate thedegassing chambers into the same structure as the cell stack also havebeen disclosed. However, none of these designs addresses the otherdrawbacks described above.

For example, WO 2006/060912 describes a design that incorporates thedegassing chambers into the same structure as the cell stack, which alsohas manifolds above the half cell chambers to collect gas-liquidmixtures from the individual half cell chambers, and bottom manifolds todistribute degassed liquid from the degassing chamber back to theindividual half cell chambers. U.S. Pat. No. 2,075,688 and US20070215492 also describe designs that incorporate the degassingchambers into the same structure as the cell stack, and also teach theuse of manifolds beneath the half cell chambers to distribute degassedliquid to the individual half cell chambers. While the anode and cathodehalf cells are maintained completely separate in these designs, thenumber of cells per stack is limited by the pressure drop across thehorizontal manifolds, and the limited head available in the relativelycompact module design.

In order to address the shortcomings of known practical electrolysermodules, what is needed is an inherently scalable design approach, thatprovides freedom to vary the number of cells over a wide range to meet awide range of gas production capacity, including very high gasproduction capacity, while at the same time minimizing associatedmechanical connections and assembly, eliminating requirements formechanical pumping of electrolyte, and maximizing product gas purities.Such a design, especially when further designed to provide a wide rangeof gas production capacity per cell, would be especially useful whenconnected to a source of electricity with variable output power, forexample, a wind farm or a solar array.

SUMMARY OF THE INVENTION

An electrolyser module comprising a plurality of structural plates eachhaving a sidewall extending between opposite end faces with a half cellchamber opening and at least two degassing chamber openings extendingthrough the structural plate between the opposite end faces. Thestructural plates are arranged in face to face juxtaposition betweenopposite end pressure plates. Each half cell chamber opening at leastpartially housing electrolytic half cell components comprising at leastan electrode and a bipolar plate in electrical communication with theelectrode and a membrane. The structural plates and half cell componentsdefine an array of series connected electrolytic cells surmounted by atleast first and second degassing chambers each having an upper sectionabove a lower section. The structural plates define at least when inface to face juxtaposition, respective gas-liquid passages extendingbetween a top part of the half cell chambers and a bottom part of theupper section of the first and second degassing chambers to providefluid communication between an anode part of the electrolytic cells andthe first degassing chamber and between a cathode part of theelectrolytic cells and the second degassing chamber. The structuralplates further define, at least when in face to face juxtaposition,respective discrete degassed liquid passages extending between a bottompart of the lower section of the first and second degassing chambers anda bottom part of the half cell chambers for degassed liquid return fromthe first and second degassing chambers respectively to the anode andcathode parts of the electrolytic cells. The electrolyser module furthercomprises respective gas discharge passages in fluid communication withthe first and second degassing chambers and at least one feed waterpassage extending therethrough and fluidly communicating with at leastone of the first and second degassing chambers for gas discharge fromthe first and second degassing chambers and for feed water introductioninto at least one of the first and second degassing chambers. Theelectrolyser module further comprises at least one liquid communicationpassage for liquid communication between the at least first and seconddegassing chambers.

An electrolyser module comprising a plurality of structural plates eachhaving a sidewall extending between opposite end faces with a half cellchamber opening and at least two degassing chamber openings extendingthrough the structural plate between the opposite end faces. Thestructural plates are arranged in face to face juxtaposition betweenopposite end pressure plates. Each half cell chamber opening at leastpartially housing electrolytic half cell components comprising at leastan electrode and a bipolar plate in electrical communication with theelectrode and a membrane. The structural plates and half cell componentsdefine an array of series connected electrolytic cells surmounted by atleast first and second degassing chambers each having an upper sectionabove a lower section. The structural plates define at least when inface to face juxtaposition, respective gas-liquid passages extendingbetween a top part of the half cell chambers and a bottom part of theupper section of the first and second degassing chambers to providefluid communication between an anode part of the electrolytic cells andthe first degassing chamber and between a cathode part of theelectrolytic cells and the second degassing chamber. The structuralplates further define, at least when in face to face juxtaposition,respective discrete degassed liquid passages extending between a bottompart of the lower section of the first and second degassing chambers anda bottom part of the half cell chambers for degassed liquid return fromthe first and second degassing chambers respectively to the anode andcathode parts of the electrolytic cells. The electrolyser module furthercomprises at least one intermediate pressure plate interspersed betweenthe structural plates along the length of the electrolyser module. Eachof the at least one intermediate pressure plate comprises opposite endfaces with a sidewall extending therebetween, The intermediate pressureplate defines first and second degassing chamber openings or throughholes extending between its opposite end faces for fluidly communicatingrespectively with the first and second degassing chambers for receivinggas therefrom. The electrolyser module further comprises respective gasdischarge passages in fluid communication with the first and seconddegassing chambers and at least one feed water passage extendingtherethrough and fluidly communicating with at least one of the firstand second degassing chambers for gas discharge from the first andsecond degassing chambers and for feed water introduction into at leastone of the first and second degassing chambers. The electrolyser modulefurther comprises at least one liquid communication passage for liquidcommunication between the at least first and second degassing chambers.

DESCRIPTION OF DRAWINGS

Preferred embodiments of the present invention are described below withreference to the accompanying illustrations in which:

FIG. 1 a is an assembly view of about half of an electrolyser module inaccordance with the present invention;

FIG. 1 b is a side sectional view of selected portions of a fullelectrolyser module in accordance with the present invention;

FIG. 1 c is an isometric view illustrating part of an assembledelectrolyser module;

FIG. 2 shows further detail of the degassing chamber part of anelectrolyser module in accordance with the present invention;

FIG. 3 shows the front face of an embodiment of a structural plate inaccordance with the present invention;

FIGS. 4( i) to 4(iv) show examples of structural plates for anelectrolyser module with different passage configurations in accordancewith the present invention;

FIGS. 5( i) to 5(vi) show examples of potential electrical connectionconfigurations for an electrolyser module in accordance with the presentinvention;

FIGS. 6( i) and 6(ii) show two alternative sets of structural plates inaccordance with the present invention;

FIG. 7 shows an embodiment of a draining system for an electrolysermodule in accordance with the present invention;

FIG. 8 shows a schematic diagram of an electrolyser system in accordancewith the present invention;

FIG. 9 is a front view illustrating an alternate embodiment of an endpressure plate according to the present invention;

FIG. 10 is a front view of an alternate embodiment of an intermediatepressure plate according to the present invention;

FIG. 11 is a view corresponding to FIG. 10 but showing its relationshipto a first structural plate; and

FIG. 12 is an assembly view of about half of an electrolyser module inaccordance with the present invention, showing embodiments of liquidcommunication passages.

DESCRIPTION OF PREFERRED EMBODIMENTS

An electrolyser module in accordance with an aspect of the presentinvention is shown generally at 1 in FIGS. 1-3. FIG. 1 a shows abouthalf of an electrolyser module with 4 cells for illustrative purposesonly; the other half of the electrolyser module would be a mirror image(on either side of feature 12, which in this case represents themidpoint of the electrolyser module). In practice, typically greaternumbers of cells would be incorporated. For further clarity, FIG. 1 bshows an axial view corresponding to section A-A in FIG. 1 a, extendedto show selected portions of a full electrolyser module, and FIG. 1 cshows an isometric view of a section of an electrolyser module.Electrolyser module 1 includes structural plates 10, end pressure plates11, intermediate pressure plate 12, anodes 13, cathodes 14, membranes15, current carriers 16 and bipolar plates 17. In the embodiment shownin FIGS. 1 a, 1 b and 1 c, there are two main types of structural plates10: cathode structural plates 10 a and anode structural plates 10 b.Additional special structural plates 10 c and 10 d are located betweenthe adjacent cathode structural plates 10 a, and one side of theintermediate pressure plate 12 and one of the end pressure plates 11,respectively. Suitable sealing gaskets (not shown) also are understoodto be included. Electrolyser module 1 thus comprises a plurality ofelectrolysis cells 18 and associated degassing chambers 19. Theelectrolysis cells 18 preferably are located at the bottom part of theelectrolyser module 1, and the associated degassing chambers 19preferably are located at the top part of the electrolyser module 1,surmounting the electrolysis cells 18. The electrolysis cells comprisecathode and anode half cell chambers 20 a and 20 b defined by twoadjacent structural plates, as well as a cathode 14, an anode 13, amembrane 15, and the current collectors 16. Bipolar plates 17 physicallyseparate and electrically connect adjacent cells. As shown in FIGS. 1 a,1 b and particularly 1 c, each cathode half cell chamber 20 a isdirectly connected to the hydrogen degassing chamber 19 a by agas-liquid passage 21 a, and a degassed liquid passage 22 a. Similarly,each anode half cell chamber 20 b is directly connected to the oxygendegassing chamber 19 b by a gas-liquid passage 21 b, and a degassedliquid passage 22 b. Consequently, the internal fluid flow requirementsfor electrolyser module 1 are provided for by the features of each halfcell, rather than by features extending across all the cells or a largenumber of cells, such as gas-liquid manifolds and degassed liquidmanifolds, which present an increasing pressure drop as their length isincreased. Electrolyser module 1 thus is an inherently scalablestructure, in that not only the number of cells and the size of thedegassing chambers, but also the fluid circulation capabilities,automatically scale with the number of cells in the electrolyser module.Furthermore, electrolyser module 1 does not require a mechanicalelectrolyte pump(s) to facilitate circulation of fluids between the halfcell chambers and the degassing chambers; the fluid flows are driven bygas buoyancy and gravity head, and thus are self-regulating in that theyautomatically vary with the gas production rates. (Most commercialelectrolyser modules utilize mechanical electrolyte pumps to facilitatecirculation of fluids (electrolyte and electrolyte-gas mixtures) in theelectrolyser module.)

The cell portion of the electrolyser module assembly can generally be asis known in the art. The boundaries of each cell are defined by bipolarplates 17, which are thin solid plates made of a suitably conductive andcorrosion-resistant material such as nickel to provide electronicconduction of electricity between adjacent cells. Electrical connectionbetween bipolar plates 17 and each of the cathode and the anode in agiven cell may be accomplished with suitable electronically conductingcurrent carriers 16, which allow for even current carrying anddistribution across the faces of the electrodes 13, 14 and bipolarplates 17, as well as relatively unimpeded fluid flow through the halfcell chambers 20. Examples of suitable materials and configurations forcurrent collectors are known in the art, including woven nickel layersor nickel foam. In some embodiments, the bipolar plates 17 can bedimpled, corrugated, etc., and thereby can provide direct connectionbetween the cathodes 14 and anodes 13 without using separate currentcarriers 16. In this approach without separate current carriers, thedimpled, corrugated, etc. portions can optionally be welded to thecathodes 14 and anodes 13 to provide one-piece sub-assemblies. Themembranes 15 are located between and in close proximity to or in contactwith the respective adjacent cathodes 14 and anodes 13. The membranes 15thus lie essentially in the middle of the cells 18, and separate therespective anode and cathode half cells. The membranes 15 may bemicro-porous diaphragms which are fully wetted during operation toexclude gases, or non-porous ion exchange membranes. The cathodes 14 andanodes 13 can be as is generally known in the art, for example,catalytic metal coatings coated onto a suitable substrate, for example,nickel mesh. Electrical current is supplied to the cell portion ofelectrolyser module 11 by, for example, a DC power supply, viaelectrical connections to end pressure plates 11 and optionallyintermediate pressure plate 12. One possible electrical configuration isshown in FIG. 1 b, with negative and positive current carryingconnections to end pressure plates 11, and a non-current carrying groundconnection to intermediate pressure plate 12.

During operation of electrolyser module 1, hydrogen gas is evolved atthe cathodes and is released into the cathode half cell chambers 20 a,where it forms hydrogen gas-liquid electrolyte mixtures that rise andtravel to the hydrogen degassing chamber 19 a through the gas-liquidpassages 21 a. Similarly, during operation, oxygen gas is evolved at theanodes and is released into the anode half cell chambers 20 b, where itforms oxygen gas-liquid electrolyte mixtures that rise and travel to theoxygen degassing chamber 19 b through gas-liquid passages 21 b. In bothcases, the liquid is separated from the gas in the degassing chambers,and degassed liquid returns to the respective half cell chambers 20 aand 20 b through degassed liquid passages 22 a and 22 b. Separatedhydrogen gas exits through separated hydrogen gas outlet 25 in thehydrogen degassing chamber; separated oxygen gas exits through a similarseparated oxygen gas outlet in the oxygen degassing chamber (not shown).

Further detail of a hydrogen degassing chamber in the electrolysermodule assembly according to the current invention is shown in FIG. 2.Only a section of the hydrogen degassing chamber 19 a corresponding to afew structural plates 10) is shown in FIG. 2, which is for illustrativepurposes only. The configuration and size of the oxygen degassingchamber 19 b can be, but are not necessarily, similar to those of thehydrogen degassing chamber 19 a. It is to be understood that the use ofmore than one hydrogen degassing chamber and similarly the use of morethan one oxygen degassing chamber can be contemplated. The degassingchamber volume is defined by the series of adjacent degassing chamberopenings (19 a or 19 b) in the plurality of structural plates 10.Cooling conduits such as cooling coils or, as illustrated, cooling tubes30 for cooling the incoming gas-liquid mixtures as may be required arelocated in the lower section of the degassing chambers 19 a and 19 b.The electrolyser module 1 includes respective gas discharge and feedwater passages extending therethrough and fluidly communicating with thedegassing chambers 19 a and 19 b for gas discharge from each degassingchamber and for feed water introduction into at least one of thedegassing chambers, preferably the hydrogen degassing chamber 19 a(since water is consumed in the cathodic hydrogen generation reaction).Water addition means (not shown) add water through the feed waterpassages as required to one or more of degassing chambers 19 a and 19 b,where the added water is mixed thoroughly with electrolyte beforedistribution to the half cell chambers 20 a and 20 b (via degassedliquid passages 22 a and 22 b). Thus, the degassing chamber 19 a hasmultiple functions: firstly, to separate the incoming gas-liquidmixtures into separated gas and separated liquid; also, to cool thefluids as may be required, for example to maintain appropriate celloperating temperatures; and further, to provide a volume for mixing offeed water with electrolyte before distribution to the respective halfcell chambers. During operation of the electrolyser module 1 a, thegas-liquid mixture from the corresponding cathode half cell chambersenters the hydrogen degassing chamber 19 a from gas-liquid passages 21a. Although only one gas-liquid passage per cathode half cell is shown,it is understood that a plurality of gas-liquid passages per half cellmay be used. The gas portion of the incoming gas-liquid mixture rises inthe degassing chamber volume, and is thereby separated from the liquidportion of the incoming gas-liquid mixture. Means for promotinggas-liquid separation, such as baffles, also can be used to promotegas-liquid separation in a given degassing chamber volume. The separatedand partially cooled gas is removed from the degassing chamber 19 a inthe electrolyser module 1 via at least one separated gas dischargeoutlet 25 at one or more suitable locations near the top of thedegassing chamber 19 a. The separated and cooled liquid is returned tothe cathode half cell chambers via the corresponding degassed liquidpassages 22 a. Although only one degassed liquid passage per cathodehalf cell is shown, it is to be understood that a plurality of degassedliquid passages per cathode half cell may be used.

In the embodiment illustrated in FIG. 2, flow directing means 35 areadded to direct the incoming gas-liquid mixture from the gas-liquidpassages along the length of the degassing chamber. This configurationis preferred when the point of connection of the gas-liquid passage 22 ato degassing chamber 19 a lies below the intended range of operatingliquid levels. Benefits of this configuration include: (i) extensive“automatic” mixing of feed water added to degassing chamber 19 a toenable uniform distribution to all the half cells, even when the feedwater is introduced above the liquid level; (ii) avoidance ofdisturbance of the gas layers at the top of degassing chamber 19 a byincoming gas-liquid mixtures, and improved gas-liquid separationefficiency; (iii) improved heat transfer coefficients for the coolingconduits in degassing chamber 19 a; and, (iv) avoidance of excessive gascarry under back to the half cells. These benefits are accrued whilemaintaining good fluid flow across the width of degassing chamber 19 a,since the points of connection of gas-liquid passages 21 a and degassedliquid passages 22 a are on opposite sides of degassing chamber 19 a.Fluid flow modeling indicates that without any flow directing means,there is very little flow along the length of degassing chamber 19 a.The flow directing means 35 as shown comprises a “hood” over the pointof entry of gas-liquid mixture into degassing chamber 19 a, consistingof at least one and up to three “walls” and a “roof”, with the openingto the degassing chamber corresponding to the intended direction offluid flow. The “walls” and “roof” may be angled or otherwise orientedas may be appropriate to obtain desired fluid flow patterns. While the“hood” structure is relatively easily manufactured and presentsrelatively little resistance to fluid flow, it is to be understood thatother flow directing means can be used, for example, a bent tubeextending from the gas-liquid passage into the degassing chamber 19 a.

The electrolyser module corresponding to the embodiment illustrated inFIG. 2 is inherently highly scalable, since the same general fluid flowpatterns can be expected over a wide range of the number of cells in themodule, and the degassing chamber volume and degassing capacity scaleautomatically with the number of cells, or more particularly, with thenumber of structural plates in the electrolyser module. Furthermore,even with few and significantly separated points of feed water addition,and even with feed water introduction via the top of the liquid, goodmixing of feed water in the degassing chamber and uniform distributionto the connected half cells can be achieved over a wide range of thenumber of cells in the electrolyser module. Similarly the coolingcapacity of the module also is scalable with the number of cells in theelectrolyser module by adding cooling conduit length proportionally, andalso optionally varying the coolant flow rate.

A structural plate for an electrolyser module according to the currentinvention is shown in FIG. 3. FIG. 3 shows a preferred embodiment inwhich each structural plate 10 comprises a body having a sidewallextending between opposite end faces and defines one half cell chamberopening 20 and two degassing chamber openings 19 a and 19 b; it isunderstood that each structural plate can define more than one of eachtype of opening. Structural plates associated with anode half cells arecalled anode structural plates, and structural plates associated withcathode half cells are called cathode structural plates. Each structuralplate 10 also comprises one or more gas-liquid passages 21, whichdirectly connect the top part of the half cell chamber opening 20 to oneof the degassing chamber openings 19 a and 19 b. Each structural plate10 further comprises one or more degassed liquid passages 22, whichdirectly connect the bottom part of the half cell chamber opening 20 toone of the degassing chamber openings 19 a and 19 b. Although only onegas-liquid passage 21 and one degassed liquid passage 22 are shown inFIG. 3, it is to be understood that a plurality of each type of passagecan also be used. In anode structural plates, the degassing chamber thatis directly connected to the anode half cell chamber is an oxygendegassing chamber, and in cathode structural plates, the degassingchamber that is directly connected to the cathode half cell chamber is ahydrogen degassing chamber.

The degassing chamber openings 19 a and 19 b may be considered to havean upper section and a lower section. Separated gas rises into the uppersection and degassed liquid descends into the lower section. Thedischarge opening of the gas-liquid passage 21 is preferably located toavoid introducing gas into the degassed liquid and liquid into the gas.Accordingly the gas-liquid passages 21 enter the degassing chambers 19 aand 19 b at a location above the entrance to the degassed liquidpassages 22 but below the upper section of the degassing chamberopenings 19 a and 19 b. In other words the discharge opening istherefore in the lower (preferably lowest) region of the upper section.

The structural plate 10 further comprises a fluid flow directing means35 at the point of connection of the gas-liquid passage 21 to degassingchamber opening 19 a; similar fluid flow directing means can also beused if the gas-liquid passage 21 connects to degassing chamber opening19 b. In this embodiment, fluid flow directing means 35 comprises a“hood” over the point of connection of the gas-liquid passage 21 to thedegassing chamber opening 19 a. The “hood” consists of at least one andup to three “walls” and a “roof”, with an opening corresponding to theintended directions of fluid flow. While the “hood” structure isrelatively easily manufactured, presents relatively little resistance tofluid flow, and does not adversely affect the structural integrity ofthe surrounding areas, it is to be understood that other fluid flowdirecting means can be used; for example, a bent tube shape extendingfrom the gas-liquid passage into degassing chamber opening 19 a.

If the electrolyser module is to be operated with substantially equaloxygen side and hydrogen side pressures, the bottom portions ofdegassing chambers 19 a and 19 b can be in fluid (liquid only)communication, e.g., via one or more liquid communication passages.Examples of preferred embodiments of liquid communication passages are:internal passages in one of more of intermediate pressure plate 12, endpressure plates 11 and special structural plates 10 c and 10 d; passagesformed by surface channels in at least one of the opposite end faces ofone or more of intermediate pressure plate 12 and end pressure plates11, at least when in face-to-face juxtaposition with adjacent plates(special structural plates 10 c and 10 d, respectively); passages formedby surface channels in at least one of the opposite end faces of one ormore of special structural plates 10 c and 10 d, at least when inface-to-face juxtaposition with adjacent plates (intermediate pressureplate 12, end pressure plate 11, respectively, or structural plates 10 aand 10 b); and, external passages, comprised of, e.g., tube or pipe, inliquid communication with degassing chambers 19 a and 19 b via internalpassages in intermediate pressure plate 12 or end pressure plate 11.Illustrative examples shown in FIG. 12 are: (i) features 28 a and 28 bin special structural plates 10 c; (ii) features 29 a and 29 b inspecial structural plates 10 d; and, (iii) feature 40, which is tube orpipe in liquid communication with the lower portion of the hydrogendegassing chamber and the oxygen degassing chamber via respectiveinterior passages in intermediate pressure plate 12; (iv) features 45 aand 45 b in intermediate pressure plate 12 and features 46 a and 46 b inend pressure plate 11. Features 28 a, 28 b, 29 a, 29 b, 45 a, 45 b, 46 aand 46 b are shown as surface channels, but could be correspondinginternal passages. It is to be understood that the actual path of theliquid communication passages and the relative size of the liquidcommunication passages need not be exactly as shown in the illustrativecase of FIG. 12, and further that appropriate combinations of features28 a, 28 b, 29 a, 29 b, 40, 45 a, 45 b, 46 a and 46 b may be used. Incertain embodiments, some of features 28 a and 28 b, 29 a and 29 b, and45 a and 45 b can included on both sides of special structural plates 10c and 10 b, and intermediate pressure plate 12, respectively. Suchliquid communication between degassing chambers 19 a and 19 b mayfacilitate (near) equalization of the liquid levels in the degassingchambers, and thereby the hydrogen side and oxygen side pressures duringoperation, and further, may facilitate rapid, passive response forcorrection of operational upsets.

Different structures can be contemplated for the passages for gas-liquidtransfer 21 and the degassed liquid passages 22 including; (i) surfacechannels, i.e., channels defined in the surface of structural plate 10;(ii) internal passages, i.e., passages defined in the interior ofstructural plate 10; (iii) surface channels that become internalpassages in certain sections; and, (iv) internal passages that becomesurface channels in certain sections. In FIG. 3, the passages are shownas comprising surface passages, except near the points of connection tothe half cell chamber opening 20, where the surface passages becomeinternal passages in order to allow for passage under sealing gasketholding features. This approach aids in manufacturability when thepassages are long and/or have complex shapes. For large parts, asrequired to achieve high gas production capacities, the use ofstructures (i) and (iii) above (surface passages and/or surface passagesthat become internal passages in certain sections) is preferred andlikely is required for manufacturability. It is to be understood that inprinciple, any of the four different passage structures contemplated canbe used for any given passage, and combinations of the differentapproaches for the passages can be used in any given structural plate.It also is to be understood that in the case of surface passages, thepassages can be formed in one or both opposing surfaces of adjacentstructural plates. It is to be further understood that while each set ofgas-liquid passages 21, and degassed liquid passages 22, typically aredefined in a single structural plate, more complex structures, in whichpassages cross multiple structural plates with appropriate sealingbetween structural plates, also can be considered. For example, thegas-liquid passage in a given structural plate can become an internalpassage at an appropriate point in its path, and then travel through thewidth of its structural plate to the opposite face of the structuralplate, then through the width of an adjacent structural plate, andfinally onto the near face of the next structural plate, where thepassage continues its path as a surface passage to the correspondingdegassing chamber opening, optionally becoming an internal passage nearthe point of connection to the degassing chamber opening. Appropriatesealing is included at the points where the passage crosses betweenadjacent structural plates. A similar structure can be used for thedegassed liquid passages. It is to be understood that the gas-liquidpassages and the degassed liquid passages can cross multiple plates.Note that multi-plate configurations also are inherently scalable, anddo not include common internal fluid collection manifolds or externalpiping for gas-electrolyte or electrolyte transfer.

The lengths and cross-sectional areas of the passages for gas-liquidtransfer 21 and the degassed liquid passages 22 are the primarydeterminants of stray currents (also known as bypass currents) and thecurrent efficiency of the electrolyser module. The main path for currentflow in an electrolyser module is through the cells, which is thedesired gas-producing path. In the current embodiment, ionic current canflow through the electrolyte in the gas-liquid passages and in thedegassed liquid passages. The amount of this so-called stray current orbypass current that bypasses the cell path via the gas-liquid passagesand the degassed liquid passages depends on the relative resistances ofthe cell path and the passages. Deleterious effects of stray currentsinclude loss of gas-producing current (lower current efficiency) andpotential stray current corrosion of metal (especially steel) partsexposed to electrolyte. For any given electrolyte concentration andtemperature, the resistance of the passages depends on: (i) the lengthof the passages; (ii) the cross-sectional area of the passages; and,(iii) the void fraction (gas fraction) for the fluids in the passages.

The lengths and cross-sectional areas of the gas-liquid passages 21 andof the degassed liquid passages 22 also are key determinants of fluidflow rates and void fractions (indicative of the extent of gas hold up)in the electrolyser module. While stray currents decrease as passagelengths are increased and as passage cross sectional areas aredecreased, conversely fluid flows are increasingly restricted.Restriction of fluid flows is of course undesirable, and sufficientliquid circulation is required in the electrolyser module, for example,to maintain low void fractions and good heat transfer characteristics.Consequently, design of the electrolyser module requires a compromisebetween control of stray currents and facilitating good fluid flows.

In the current embodiment, the passage cross sectional areas areenlarged by using a “slot” geometry; i.e., although the passagedimension corresponding to the thickness of the structural plate islimited, a slot geometry that is elongated in the perpendiculardirection of the same surface can be used to provide a significant crosssectional area, which in turn allows for good fluid flow and circulationin the electrolyser module. The corresponding passage length is selectedso as to increase the electrical resistances associated with the passagepaths, and achieve current efficiencies of, e.g., 99% or higher (i.e.,99% or more of the current passed through the electrolyser module goesthrough the cells and produces gases). The passages can be elongatedthrough the use of various passage path geometries. The void fraction inthe degassed liquid passages typically can be expected to be very low,and the resistivity of the fluid in the passages will be close to thatof the liquid electrolyte. The void fraction in the gas-liquid passagestypically can be expected to be significant, e.g., 0.1 to 0.5, duringoperation of the electrolyser module. Thus, the degassed liquid passagestypically are longer and/or have a smaller cross-sectional area than thegas-liquid passages. Alternatively, a greater number of gas-liquidpassages can be used. Generally speaking, the use of complex passageconfigurations may be required in order to attain high currentefficiencies; this is most important for large electrolyser modules withhigh gas production capacities and correspondingly large passage crosssectional areas. In the embodiment shown in FIG. 3, the ratio of maximumhydrogen generation rate per half cell, i.e., the maximum hydrogen flowrate through the gas-liquid passage (in Nm³/h) to the cross sectionalarea of the gas-liquid passage (in cm²) is 0.83, (maximum hydrogengeneration rate per hydrogen half cell of 2.5 Nm³/h and cross sectionalarea of the gas-liquid passage of 3 cm²) and the passage aspect ratio,i.e., the ratio of the length of the gas-liquid passage to its crosssectional area is 23. In cases where the cross sectional area of thegas-liquid passage varies or there is more than one gas-liquid passage,an average value could be used as an estimate. Electrolyser moduledesigns with significantly larger values of these ratios can beconsidered to have significantly restricted fluid flows and fluidcirculation, and concomitant potentially serious issues with heatremoval from and excessive voiding of the half cell chambers. Arecommended maximum value for the ratio of the maximum hydrogengeneration rate (in Nm³/h) to the cross sectional area of the gas-liquidpassage (in cm²) is about 2. A recommended maximum value of the aspectratio of the hydrogen gas-liquid passage is about 30.

Examples of structural plates 10 for an electrolyser module according tothe current invention with different passage configurations are shown inFIG. 4. Most of the lengths of the passages are surface passages, whichenables the use of long passages with complex shapes. The surfacepassages can optionally become internal passages in the vicinities ofthe points of connection to the half cell chamber opening 20 and to thedegassing chamber opening 19 a to facilitate holding features forlocating and holding sealing gaskets. In the embodiment shown in FIG. 4i, the gas-liquid passage 21 i extends from the top part of half cellchamber opening 20 upward and over the top of the degassing chamberopening 19 a, before connecting to the bottom part of the degassingchamber opening 19 a. The degassed liquid passage 22 i extends from theopposite side of degassing chamber opening 19 a, down and around theperiphery of the half cell chamber opening 20 on the same side of thestructural plate before connecting to the bottom part of the half cellchamber 20. In the embodiment shown in FIG. 4 ii, the gas-liquid passage21 ii extends from the top part of the half cell chamber 20substantially vertically upward from the half cell chamber opening, andthen returns substantially downward before connecting to the bottom partof the degassing chamber opening 19 a. In the embodiment shown in FIG. 4iii, the gas-liquid passage 21 iii extends from the top part of halfcell chamber opening 20 and under the corresponding degassing chamberopening 19 a, joining the bottom part of the degassing chamber opening19 a at the far side. The degassed liquid passage 22 iii extends fromthe opposite side of the degassing chamber opening 19 a, down and aroundthe periphery of the half cell chamber opening 20 on the opposite sideof the structural plate before connecting to the bottom part of the halfcell chamber opening 20. In the embodiment shown in FIG. 4 iv, thegas-liquid passage 21 iv extends from the top part of the half cellchamber opening 20 and part way under the corresponding degassingchamber opening 19 a, then doubles back over itself before joining thebottom part of the degassing chamber opening 19 a at the near side.

The structural plates 10 preferably are made of a suitable electricallyinsulating plastic or fiber-reinforced plastic material that is inert toelectrolyte (e.g., an aqueous solution of 25% to 35% KOH) and gases(e.g., oxygen, hydrogen, nitrogen, or chlorine), as well as otherpotential materials to which it may be exposed, such as ammoniumhydroxide. Examples of suitable thermoplastic materials includepolyphenylene oxide (PPO), polyphenylene sulphide (PPS) and the like,and in particular polysulfone. Thermoset plastic materials also may beused. The plastic can be reinforced by fibers such as Kevlar or glass.The plates may be manufactured by conventional molding techniques, suchas injection molding or casting, or by conventional machiningtechniques, such as milling and drilling. Manufacturing by moldingtechniques enables consideration of reduction of material in thestructural plates 10 through inclusion of additional openings, coring,or the like (for moldability, weight, cost, and potential strain reliefconsiderations), as well as the use of complex shapes for the body, thehalf cell chamber openings, the degassing chamber openings, thegas-liquid passages, and the degassed liquid passages. For example,stray current blocking walls can be straightforwardly added to thebottom portion of one or more of the degassing chamber openings(extending at higher than the highest anticipated operating liquidlevel) of special structural plates that can be used at appropriatepoints in an electrolyser module to control stray current flows.Furthermore, given potential limitations in the sizes of parts that canbe manufactured, forming of structural plates in multiple portions thatcan be interconnected or joined to form a complete structural plate alsois contemplated.

The structural plates further comprise first and second opposingsurfaces which define holding features for locating and holdingfunctional cell components, including electrodes (anodes and cathodes),membranes, and bipolar plates. These holding features enable properlocation and alignment of functional components in an assembledelectrolyser module. Each holding feature for a given functionalcomponent comprises an “L” shaped seat, which surrounds thecorresponding half cell chamber opening. Each “L” shaped seat comprisesa seat back and a seat wall, which preferably are orthogonal to oneanother. Each “L” shaped seat faces inward toward the half cell chamberopening. The functional components are sized to “sit” fully in theseats, such that one planar surface of the electrode, membrane orbipolar plate is generally in the same plane as the surface of thestructural plate in which it is supported.

The structural plates further comprise first and second opposingsurfaces which define holding features for locating and holding sealinggaskets. The seals may be as is known in the art to prevent leakage ofgas, liquid, or gas-liquid mixtures (a) from inside the electrolysermodule to the outside; and, (b) from inside the chambers or passages inwhich they are contained. Such seals may include, but are not limitedto, for example flat gaskets or preferably o-rings. In the case of flatgaskets, other features such as ribs may be added to one or more of theopposing surfaces. For some features, especially where sealing is notcritical, interlocking features or crush ribs, without sealing gaskets,may also be used. Typically, the main holding features for locating andholding sealing gaskets are firstly those surrounding all or at leastpart of one or more of degassing chamber openings, those surrounding thehalf cell chamber opening, and also the main exterior seals surroundingall the fluid-containing volumes, including all of the two or moredegassing chamber openings, the half cell chamber opening, the one ormore gas-liquid passages and the one or more degassed liquid passages.The use of multiple seals and holding features for locating and holdingsealing gaskets also can be contemplated.

When structural plates 10 are arranged together to form the electrolysermodule 1 in the embodiment of FIG. 1, the first surface of onestructural plate is aligned with the second surface of the adjacentstructural plate such that the functional components and sealing gasketsare aligned with their respective holding features, in order thatcathodes 14, membranes 15, and anodes 13 are supported by theirrespective structural plates, and the half cell chambers, degassingchambers, and the perimeter of the electrolyser module are sufficientlysealed.

The sizing of the structural plate 10 in the embodiments of FIGS. 3 and4 depends on the required sizes and shapes of the half cell chamberopening, degassing chamber openings, and to some extent, on the requiredsizes and paths of the gas-liquid passages and the degassed liquidpassages. The half cell chamber opening is sized according to therequired or appropriate active electrode area for a given operatingrange of current densities and number of cells in the electrolysermodule. The anode and cathode nominal (projected geometric) surfaceareas, as well as the nominal membrane surface areas, generally aremaintained equal, but this is not necessarily a requirement. The sizes,shapes and configurations of the degassing chamber openings and thegas-liquid passages and for degassed liquid passages are thensubsequently sized as required to obtain target liquid flow rates, voidfractions, and gas-liquid separation efficiency.

The overall thickness of the structural plate 10 in the embodiments ofFIGS. 3 and 4, as measured between its opposing surfaces, may varydepending on the application, part diameter, material(s) ofconstruction, operating pressure, operating temperature, manufacturingmethod, etc., but must be sufficient to accommodate the gas-liquidpassage 19 and degassed liquid passage 22. For example, for waterelectrolysis, the overall thickness may be in the range of 0.4 to 1.5cm, and more preferably, 1.0 to 1.5 cm for larger diameter structuralplates. Notably, the actual plastic thickness at any given point in alarger diameter structural plate typically is less than the overall partthickness, due to manufacturability considerations (e.g., formanufacturing by injection molding).

In general, shapes without sharp corners are preferred for the body ofstructural plate 10, the half cell chamber opening 20, and the degassingchamber openings 19 a and 19 b in the embodiments of FIGS. 3 and 4, inorder to avoid stress concentrations. Specific shapes depend on thedesign requirements, for example to accommodate different passage paths,to achieve required structural strength, and to accommodate sizesrequired to achieve good fluid flows and gas-liquid separation, etc. Forexample, the degassing chamber openings 19 a and 19 b preferably have anirregular shape with rounded corners, but also may have a rectilinearshape with rounded corners or a rounded shape.

Electrolyser module 1 is shown in the embodiment of FIG. 1 b as beingheld together between end pressure plates 11 on either end. Acompression system to apply sealing pressure to either end of modulethrough end pressure plates 11, as is well known in the art, also isused. For example, a number of tie rod assemblies using Bellevillewasher stacks, with the tie rods located either around the outside ofthe main body of the electrolyser module, and/or going through the bodyof the electrolyser module, can be used to maintain sealing pressure onthe module. The end pressure plates 11 comprise a body having a sidewallextending between opposite end faces and can be made of steel, stainlesssteel, nickel-plated steel, nickel-plated stainless steel, nickel, ornickel alloy. The bodies of the end pressure plates 11 are electricallyconducting, and typically are used to facilitate electrical connectionto electrolyser module 1, using appropriate electrical connection meansas are known in the art.

Electrical current as applied to the cell portions of electrolysermodule 1 by, for example an external DC power supply passes through theend pressure plates as electronic current, then through the adjacentcurrent carrier 16 to the cathode 14, where electrons react with waterto produce hydrogen and hydroxyl ions. The hydroxyl ions carry thecurrent through the membrane 15 to the anode 13, where hydroxyl ionsreact to produce oxygen, water, and electrons. The current then passesas electrons through the adjacent current carrier 16 to, and thenthrough the bipolar plate 17 to the adjacent cell. Analogous processesoccur at the intermediate pressure plate 12, and also at the other endof the electrolyser module 1 (not shown), where electrons pass throughthe metallic end pressure plate 11 and then back to the external DCpower supply to complete the electrical circuit.

In the embodiment shown in FIG. 1 b, one of the end pressure plates 11and one side of the intermediate pressure plate 12 are used directly todefine one side of the end (adjacent) half cell chambers (defined bybipolar plates 17 or intermediate pressure plate 12 in the other halfcells). Special structural plates 10 d and 10 c are placed adjacent tothe other end pressure plate 11 and the other side of the intermediatepressure plate 12, respectively. These special structural plates do nothave gas-liquid passages 21 or degassing passages 22. The specialstructural plates 10 d next to the end pressure plates 11 have half cellchamber openings 20, but do not have degassing chamber openings 19. Thespecial structural plates 10 c next to the intermediate pressure plates12 have half cell chamber openings 20 and degassing chamber openings 19.The purpose of the special structural plates is to provide an opposinginsulating face opposite the channels in the surfaces of the adjacentstructural plates 10 a to form the gas-liquid passages and the degassedliquid passages.

Even with special structural plates 10 d and 10 c, the end pressureplate and the intermediate pressure plate can be used directly to defineone side of the adjacent half cell chambers (by using correspondinglythicker single current carriers 16). However, in an alternativeembodiment, bipolar plates 17 can be seated in the special structuralplates 10 d and 10 c to define one side of the adjacent half cellchambers. In this case, thinner current carriers can be used to provideelectrical connection between the bipolar plates 17, and the adjacentend pressure plates 11 and the intermediate pressure plate 12. Ofcourse, this configuration can be used at both end plates 11, and oneither side of the intermediate pressure plate(s) 12. This alternativeembodiment is advantageous in that the bodies of the end pressure plates11 and the intermediate pressure plates 12 are not exposed topotentially corrosive electrolyte.

In another alternative embodiment, appropriately sized nickel sheets orplates may be inserted into holding features in the special structuralplates 10 c and 10 d located adjacent to the end plates and the one ormore intermediate plates, or alternatively in recesses in the bodies ofthe end pressure plates and also on both opposite faces of the one ormore intermediate pressure plates, the nickel sheets or plates therebybeing located so as to face and correspond to the adjacent half cellchambers. Appropriate sealing may also be used to ensure thatelectrolyte contact is limited to the nickel sheets or plates. Thisalternative embodiment also is advantageous in that the bodies of theend pressure plates 11 and the intermediate pressure plates 12 are notexposed to potentially corrosive electrolyte. In this regard, thedegassing chamber openings in the intermediate pressure plates 12 alsocan include an insulating insert or sleeve, or alternatively, can becoated with an insulating material.

FIG. 9 is a front view illustrating an end pressure plate 11 utilizing anickel plated insert 30 mounted within a recess 32 as suggested above.FIGS. 10 and 11 are front views illustrating an intermediate pressureplate 12 utilizing a nickel plated insert 40 received in a through hole42 and retained by retaining tabs 44 secured to the intermediatepressure plate 12.

Preferably one or more intermediate pressure plates 12 are also includedin the electrolyser module; in the case of one intermediate pressureplate 12, it is preferably located at the midpoint of the electrolysermodule (i.e., with an equal number of cells on either side). The body ofthe intermediate pressure plate 12 is electrically conducting, andtypically is used to facilitate electrical connections to electrolysermodule 1. These electrical connections can be current carrying powerconnections, or non-current carrying connections for grounding purposesonly. Depending on the configurations for electrical connections to theelectrolyser module 1, connections for external piping, e.g., forcoolant circulation, feed water addition, product gas discharge outlets,inert gas introduction, connection of the lower sections of thedegassing chambers, and drains can be made to the one or more of the endpressure plates 11 and intermediate pressure plates 12. The lowersections of the degassing chambers can be connected by passages in thebody of the one or more intermediate pressure plates 12 or the body ofone or both end pressure plates 11. Additional intermediate pressureplates 12 can be included, located so as to divide the total number ofelectrolysis cells into sections containing equal numbers of cells,depending on the configuration for electrical connections to theelectrolyser module 1.

In the case of very small electrolyser modules, it may be possible toeliminate the intermediate pressure plate 12. In such a case, only thestructural plates 10 would be mounted directly between the end pressureplates 11 and connections for external piping would be made through theend pressure plates 11.

As illustrated in FIGS. 10 and 11, it isn't necessary to provide theintermediate plates 12 with gas liquid separator chamber openings. Afunction of the intermediate plates 12 is to provide a location forwithdrawal of gas from the gas liquid separator chambers on either sidethereof. This may be achieved with through holes 50 which in effect are“banjo” fittings mounted between opposite sides of the intermediateplates 12. The through holes 50 fluidly communicate with the gas liquidseparator chambers 19 a and 19 b on opposite sides thereof and withfluid conduits 52 extending generally radially from the intermediatepressure plate 11.

The intermediate pressure plates 12 comprise a body having a sidewallextending between opposite end faces that can be made of steel,stainless steel, nickel-plated steel, nickel-plated stainless steel,nickel, or nickel alloy. Two or more degassing chamber openings aredefined in the body, typically, but not necessarily, corresponding tothe degassing chamber openings in the structural plates used in the sameelectrolyser module. The intermediate pressure plates 12 also caninclude protective plastic or reinforced plastic inserts fitted into thedegassing chamber openings, to protect the body material against straycurrent corrosion. The inserts also can incorporate stray currentblocking walls, which are walls of electrically insulating material suchas plastic that block most of one or more of the degassing chamberopenings in the intermediate pressure plate 12, leaving some open spacenear the top of the degassing chamber openings to allow for gas flow.Stray current blocking walls also can be located in any of thestructural plates 10 in the electrolyser module 1, although theintermediate pressure plates 12 are a preferred location, so as to avoidinterference with feed water mixing by stray current blocking walls atpoints intermediate to feed water addition points.

There are several potential approaches to making electrical powerconnections to the electrolyser module 1 to pass current through theplurality of electrolytic cells. These approaches can generally becategorized as follows: (a) positive electrical power connection to oneof the end pressure plates 11, and negative electrical power connectionto the other end pressure plate 11; (b) negative electrical powerconnection to both end pressure plates 11; and, (c) positive electricalpower connection to both end pressure plates 11. In all the above cases,a current carrying electrical power connection can also be made to oneor more intermediate pressure plates 12. In case (a), an even number ofintermediate pressure plates 12 is used (if intermediate pressure platesare used, then at least two are required); in cases (b) and (c), an oddnumber of intermediate pressure plates 12 is used (at least oneintermediate pressure plate is required). In all cases, the intermediatepressure plates 12 preferably divide the total number of cells intosections of equal numbers of cells, and furthermore, alternatingnegative and positive electrical power connections to the intermediatepressure plates 12 are located such that negative and positiveelectrical power connections alternate over the length of theelectrolyser module 1.

Examples of electrical power connection configurations are depictedschematically in FIGS. 5( i) to 5(iv): (i) negative electrical powerconnection to one end pressure plate 11 a and positive electrical powerconnection to the other end pressure plate 11 b of the electrolysermodule 1; (ii) negative electrical power connection to one end pressureplate 11 a and positive electrical power connection to the other endpressure plate 11 b, with a non-current carrying electrical groundconnection to an intermediate pressure plate 12 at the midpoint of theelectrolyser module 1; (iii) negative electrical power connections tothe end pressure plates 11 a and 11 b, and positive electrical powerconnection to an intermediate pressure plate 12 at the midpoint ofelectrolyser module 1; and, (iv) positive electrical power connectionsto the end pressure plates 11 a and 11 b, and negative electrical powerconnection to an intermediate plate 12 at the midpoint of theelectrolyser module 1.

The use of electrical power connections to multiple intermediatepressure plates 12 in the same electrolyser module essentially splitsthe electrolyser module into two or more parallel (or separate) sets ofelectrical power connections, for example, the configurationsillustrated in FIGS. 5 (iii) to (vi). Both electronic and ionic currentare prevented from passing through intermediate pressure plates 12 bynot providing them with gas liquid separation chamber openings, andfurther by not allowing contact of metal in the intermediate pressureplates with electrolytes by using intervening plastic coating or plastic(with appropriate sealing). Potential advantages of configurations (v)and (vi) include lower stray current driving forces and availability ofmore potential external piping connection points. As depicted in FIGS. 5(iii), (v) and (vi), the negative electrical power connections can beconnected to the same electrical ground. One or more power supplies (ACto DC converters and/or DC to DC converters) can be used to supply DCelectricity to an electrolyser module via the electrical powerconnection configurations described above.

External piping connections generally are made to the negative orgrounded intermediate pressure plate(s) 12 or the end plates 11.Illustrative examples of such external piping include: (a) eachdegassing chamber has one or more gas outlets, which are located in oneor more intermediate pressure plates, or in one or both end pressureplates; (b) the degassing chambers can contain one or more sets ofcooling conduits, which are connected to one or more external coolantcirculation loops through one or more intermediate pressure plates, orthrough one or both end pressure plates; (c) the degassing chambers cancontain means of adding feed water, which are connected to one or moreintermediate pressure plates, or one or both end pressure plates; (d)sensors (for level, temperature, pressure, or other measurements) orsensor reservoirs are connected to the degassing chambers through one ormore intermediate pressure plates, or through one or both end pressureplates; and, (e) the lower sections of the degassing chambers areconnected to one another by external piping through one or moreintermediate pressure plates or through one or both end pressure plates.

FIGS. 6( i) and 6(ii) show side views of two alternative sets ofstructural plates, each set being comprised of a cathode structuralplate (10 a(i) and 10 a(ii)) and an anode structural plate (10 b(i) and10 b(ii)). The part of the structural plates shown is at the top of thehalf cells and slightly above. In the first set of structural plates (10a(i) and 10 b(ii)), the first surface of the anode structural plate 10b(i) includes two seats, the first innermost seat being for seatinganode 13, the second or outermost seat being for seating membrane 15,which defines one side of the corresponding half cell. The opposingsurface in an assembled electrolyser module is the first surface of thecathode structural plate 10 a(i), which includes one seat for theseating cathode 14. The cathode 14 and the anode 13 thereby “sandwich”and support the membrane 15 on either side. The second surface of thecathode structural plate 10 b(i) includes a seat for the bipolar plate17, which defines the other side of the corresponding half cell,electrically connected to cathode 14 by the current carrier 16. Theopposing surface is the second surface of another anode structural plate10 b(i), which in this embodiment does not include any seats for thefunctional components. To facilitate the above description, thestructural plates 10 a(i) and 10 b(i) have arbitrarily been deemedcathode and anode structural plates, respectively. It should beunderstood that these can also be anode and cathode structural plates,respectively. Optionally, sealing gaskets (not shown) can be used forsealing the membrane 15 and the bipolar plate 17, in which case thestructural plates further comprise the corresponding holding featuresfor locating and holding the sealing gaskets.

In the second set of structural plates (10 a(ii) and 10 b(ii)), thefunctional component holding features are the same in the cathode andanode structural plates. In each plate, the membrane seats in the firstsurfaces and the bipolar plate seats in the second surfaces eacheffectively are “half seats”, which also incorporate holding featuresfor sealing gaskets to seal both faces of the membranes and the bipolarplates. If (i) the gas-liquid passages and the degassed liquid passages(not seen in FIG. 6) become internal passages near and at the points ofconnection to the half cell chamber opening and to one of the at leasttwo degassing chamber openings; and, (ii) the gas-liquid passages andthe degassed liquid passages lie completely on one side of the verticalcenter line of the structural plate, then, cathode structural plate 10a(ii) can be flipped around and used in the opposite orientation asanode structural plate 10 b(ii), which is the minor image of cathodestructural plate 10 a(ii), in order that only a single part need bemanufactured (with the exception of optional special structural plates,such as special structural plates for placement next to end pressureplates or intermediate pressure plates, or structural plates with straycurrent blocking walls).

Alternatively, in the second set of structural plates (10 a(ii) and 10b(ii)), the gas-liquid passages and the degassed liquid passages can becompletely internal passages Manufacture of such plates with completelyinternal passages can be accomplished by, for example, molding thestructural plate in two parts, a first part and a second part. The facearea of each of the first part and the second part corresponds to thefull face area of the structural plate, and the sum of the thickness ofthe first part plus the thickness of the second part makes up the fullthickness of the structural plate. Each of the first part and the secondpart has an outer end face and an inner end face, the outer end facescomprising the features of the end faces of the structural plate, andthe inner end faces comprising opposite halves of the gas-liquidpassages and the degassed liquid passages. The inner faces of the firstpart and the second part can be bonded together by means known in theart to form structural plates with gas-liquid passages and degassedliquid passage that are completely internal to the structural plates. Ifthe gas-liquid passages and the degassed liquid passages further liecompletely on one side of the vertical center line of the structuralplate, then only a single type of structural plate need be used (withthe exception of optional special structural plates, such as endstructural plates, or structural plates with stray current blockingwalls).

Embodiments of draining systems for draining of the electrolyser moduleare as described below. The draining system drains electrolyte from thecathode half cell chambers and the anode half cell chamber, for purposessuch as long term shut down, maintenance, transport, etc. It should benoted that the draining system does not affect the electrolyser moduleduring periods of operation, and can be considered as an independentpart of the electrolyser module in this regard. The draining systemcomprises two separate draining systems, a cathode draining system forthe cathode half cells, and an anode draining system for the anode halfcells.

In the first embodiment, each of the cathode and anode draining systemscomprise a plurality of connecting draining passages connecting thebottom portions of either each of the cathode half cell chambers or eachof the anode half cell chambers to one or more draining manifolds. Notethat by draining the half cell chambers, the corresponding degassingchambers also are drained, since they are connected to the half cellchambers by the degassed liquid passages and the gas-liquid passages.The cathode and anode draining systems can be, but are not necessarily,similar. The cathode draining system will be described here forillustrative purposes. The cathode draining passages comprise longpassages with relatively small cross sectional areas connecting thebottom portion of the cathode half cell chambers with one or morecathode draining manifolds. The cathode draining manifolds are locatedbelow the cathode half cell chambers in order that draining can beachieved by gravity head, and extend at least part way along the lengthof the electrolyser module. The lengths of the draining passages for thecathode half cells can be extended by using paths comprised in more thanone structural plate. In the current embodiment, the draining passagesare internal passages near the bottom part of the cathode half cellchamber, which then become surface passages that follow a long downwardpath in order to render stray current flows during operation negligible.The passage then travels through one of the adjacent anode plates to thenext cathode plate, where it once again becomes a surface passage with along path, before joining one of the cathode draining manifolds. Morethan one cathode draining manifold can be used in order to further limitstray current flows. The one or more cathode draining manifolds connectto a draining point. The draining point comprises a draining port with avalve, located in the bottom portion of one of the intermediate pressureplates or one of the end pressure plates. There can be more than onedraining point in the electrolyser module.

In the second embodiment, each of the cathode and anode draining systemsalso comprise draining channels for each half cell. Preferably, similarapproaches are used for both the cathode and anode draining systems. Thecathode draining system will be described here for illustrativepurposes. The main features of the cathode draining system are shown inFIG. 7, which shows a series of three adjacent structural plates (twocathode structural plates and one anode structural plate) in theelectrolyser module. The starting point of the cathode draining passage70 for each cathode half cell is located in the degassed liquid passage21 a, near its point of connection to the cathode half cell chamberopening 20 a. (In an alternative configuration (not shown), the cathodedraining passage 70 is connected directly at or near the bottom of thecathode half cell chamber opening 20 a.) Thus, the starting point of thecathode draining passage 70 lies underneath the cathode half cellchamber. The cathode draining passage 70 initially is an internalpassage, passing through the thickness of the cathode structural plate10 a to the opposing face of adjacent anode structural plate 10 b, whereit becomes a surface passage that creates a long path in order to renderstray current flows during operation negligible. The periphery of thearea defined by the surface passages in the face of anode structuralplate 10 b is sealed, preferably by an o-ring (not shown) that is seatedin a holding feature (not shown). The cathode draining passage 70 thenonce again becomes an internal passage, passing through the thickness ofanode structural plate 10 b to degassed liquid passage 21 a in theadjacent cathode structural plate 10 a. This multi-structural plateconfiguration is then repeated until a draining point is reached. Thedraining point comprises a draining port with internal channelsconnecting to a valve, located in the bottom portion of one of theintermediate pressure plates 12 or one of the end pressure plates 11.There can be more than one draining point in the electrolyser module. Anadvantage of the second embodiment is that there is no requirement forenlarging the bottom portions of the structural plates.

FIG. 8 shows a schematic diagram of an electrolyser system according tothe current invention. The electrolyser module 1 is electricallyconnected to a source of electricity (electric power) according to anyof the general electrical connection configurations described herein.The electricity supplied generally is DC electricity from a power supply81, which can be, for example, a DC-DC converter to provide regulated DCelectricity from a DC bus, or an AC-DC converter to provide regulated DCelectricity from an AC bus; the primary electricity source can be anelectricity grid, and/or other sources, such as a wind turbine or windfarm, or solar array or solar farm, optionally including some or all ofequipment for intermediate processes such as electricity transmission,transformation, and “unregulated” rectification. The electrolyser module1 is also connected to a feed water source 82, typically withintermediate feed water purification, e.g., by reverse osmosis and/orion exchange units. The electrolyser module 1 is further connected to acoolant source 83, which may comprise a coolant reservoir with a chilleror other means of heat removal, as well as coolant circulation and flowrate control means.

The hydrogen gas outlet may be connected to a buffer volume 84 a at thedesired pressure for any downstream application or storage; a similarbuffer volume 84 b also can be used for the oxygen gas outlet. Suchbuffer volumes can be useful for enabling continuous flow of gases fromthe electrolyser module 1 at varying flow rates.

Optionally, demisting means 85 a and 85 b, as known in the art, can beused to remove mist from the hydrogen gas, and also preferably from theoxygen gas, respectively. Separate demisting means are used for thehydrogen gas stream and the oxygen gas stream. The demisting means canbe located at any point between the respective gas outlets fromelectrolyser module 1 and buffer volumes 84 a and 84 b. Passages orconduits for return of collected liquid from the demisters to thecorresponding hydrogen or oxygen degassing chamber also can be included.Further, the demisting means can be integrated into the degassingchambers. The exiting product hydrogen gas and/or oxygen gas can also becontacted with feed water to improve demisting efficiency and tofacilitate return of removed electrolyte mist.

The electrolyser system may further comprise gas conditioning (gaspurification) means for hydrogen 86 a, and/or oxygen, 86 b, which maycomprise, e.g., catalytic purifiers and driers. Hydrogen compressionmeans 87 a and/or oxygen compression means 87 b may be includedaccording to downstream pressure requirements, and can be located eitherupstream or downstream of the gas conditioning means 86 a and/or 86 b,depending on the pressure of the gas produced by electrolyser module 1.Hydrogen transmission and/or storage means 88 a and/or oxygen storagemeans 88 b can optionally be included if there is a need to store excesshydrogen and/or oxygen for future use. Users 89 a and 89 b can be thesame entity, and can include, for example, industrial processes usinghydrogen and/or oxygen, hydrogen fuel dispensing systems forhydrogen-powered vehicles, or electricity generators.

In the case of alkaline water electrolysis, the inherently scalableelectrolyser module generally produces hydrogen gas and oxygen gas byfirst generating the hydrogen gas and oxygen gas in the plurality ofelectrolytic cells contained in the electrolyser module. The hydrogengas-electrolyte mixtures are transferred directly from the top part ofeach cathode half cell chamber to a bottom part of an upper section ofone or more hydrogen degassing chambers that are integrally contained inthe electrolyser module structure, through respective gas-liquidtransfer passages extending directly from each cathode half cell chamberto the one or more hydrogen degassing chambers. The hydrogengas-electrolyte mixture streams from each of the cathode half cells aredirected longitudinally along the length of the one or more hydrogendegassing chambers, in order to promote heat transfer to the coolingcoils and to promote mixing of feed water additions. The hydrogen gas isseparated from the liquid electrolyte in the one or more hydrogendegassing chambers to produce hydrogen gas and degassed electrolyte. Theresulting hydrogen gas is removed from the top part of the one or morehydrogen degassing chambers, and the degassed electrolyte is transferreddirectly from the bottom part of the lower section of one or morehydrogen degassing chambers to the bottom part of the cathode half cellchamber through degassed liquid passages directly connecting the one ormore hydrogen degassing chambers to each cathode half cell chamber.

Similarly, and simultaneously, the oxygen gas-electrolyte mixtures aretransferred directly from the top part of each anode half cell chamberto the bottom part of the upper section of one or more oxygen degassingchambers that are integrally contained in the electrolyser modulestructure, through respective gas-liquid transfer passages extendingdirectly from each anode half cell chamber to the one or more oxygendegassing chambers. The oxygen gas-electrolyte mixture streams from eachof the anode half cells are directed longitudinally along the length ofthe one or more oxygen degassing chambers, in order to promote heattransfer to the cooling conduits and to promote mixing of any feed wateradditions. The oxygen gas is separated from the liquid electrolyte inthe one or more oxygen degassing chambers to produce oxygen gas anddegassed electrolyte. The resulting oxygen gas is removed from the toppart of the one or more oxygen degassing chambers, and the degassedelectrolyte is transferred directly from the bottom part of the lowersection of the one or more oxygen degassing chambers to the bottom partof the anode half cell chamber through degassed liquid passages directlyconnecting the one or more oxygen degassing chambers to each anode halfcell chamber. Note that the above process also is applicable foralkaline ammonia electrolysis, in which the inherently scalableelectrolyser module produces hydrogen gas and nitrogen gas (instead ofoxygen gas), and ammonium hydroxide is present in/added to the anolyte(anode side electrolyte). Of course, the oxygen degassing chamber wouldbe a nitrogen degassing chamber in alkaline ammonia electrolysis.

The contemplated operating pressure of the electrolyser module accordingto the present invention lies between atmospheric pressure and 30 barg,depending on the application requirements and the pressure holdingcapability of the electrolyser module structure. In order to maintaininherent scalability of the electrolyser module, no additional pressurecontainment means, such as a pressure vessel surrounding theelectrolyser module, or load bearing reinforcing support or shell/sleeveis utilized. Reinforcement of each structural plate can be considered tomaintain inherent scalability of the electrolyser module.

It is preferable to start operation of the electrolyser module at theintended operating pressure, in order to avoid difficulties with largergas volumes at lower pressures. Thus, the interior pressure of theelectrolyser module is increased to the intended operating pressureprior to initial start up by introducing pressurized inert gas into theelectrolyser module. The term initial start up is understood to includeany start up after depressurization of the electrolyser module isrequired. Examples of suitable inert gases are nitrogen, argon andhelium. Once the electrolyser module is pressurized with inert gas,operation of the electrolyser module can be started; the product gas isvented until the gas purity reaches acceptable levels, which will dependon the user application.

It also is preferable that liquid level during non-operational periodsis lower than where the gas-liquid passage(s) and the degassed liquidpassage(s) in each of the structural plates meets the degassing chamber,but is higher than the top of the half cell chamber. In this way, abreak in the electrolyte path between half cell chambers is provided,while ensuring that the half cell chambers remain filled, and themembranes remain fully wetted.

Example 1

The fluid flows in a six-cell electrolyser module according to thepresent invention were modeled by computational fluid dynamics (CFD).For simplicity, the fluid flows on the hydrogen (cathodes) side only aredescribed herein. The general structural plate configuration was asshown in FIG. 3, in which the gas-liquid passage 21 extends from the toppart of half cell chamber opening 20 and partway under correspondingdegassing chamber opening 19 a, then doubles back over itself beforejoining the bottom part of degassing chamber opening 19 a at the nearside. The cell active area was 6,000 cm². The hydrogen gas-liquidseparation chamber was comprised of a main section 30 cm×50 cm×13.2 cm.The cross sectional area of the gas-liquid passages and the degassedliquid passages was 3 cm². The maximum current density was 1,000 mA/cm².This corresponds to a maximum hydrogen generation rate per half cell of2.5 Nm³/h, so the ratio of maximum hydrogen generation rate per halfcell to the cross sectional area of each gas-liquid passage was2.5/3=0.83 Nm³/h/cm². Simulations for current densities from 100 mA/cm²to 1,000 mA/cm² showed: (a) good gas-liquid separation efficiency, withnegligible gas carry under to the half cell chamber; (b) high liquidcirculation rates; (c) low void fractions at the top of the cathode halfcell chamber; and, (d) current efficiencies of 99%. The liquidcirculation rates and void fractions for each of the six cathode halfcells were within 2% of each other, which is indicative of inherentscalability.

Example 2

Next, the number of cells in the electrolyser module of Example 1 wasincreased to 50 cells. The fluid flows in the 50-cell electrolysermodule were modeled by CFD. For simplicity, the fluid flows on thehydrogen (cathodes) side only are described herein. The results for eachhalf cell were similar to those obtained for half cells in the six-cellelectrolyser module, demonstrating the inherent scalability of thedesign. For example, fluid flow rates in any of the degassed liquidpassages in the 50-cell electrolyser module were within 6% of fluid flowrates in any of the degassed liquid passages in the six-cellelectrolyser module. Furthermore: (i) fluid flow rates in degassedliquid passages were higher in the 50-cell electrolyser module than inthe six-cell electrolyser module, and (ii) the fluid flow rates in thedegassed liquid passages for each of the 50 cathode half cells werewithin 1% of each other. Similarly, void fractions at the tops of the 50cathode half cell chambers were almost equal, and also were within 5% ofthe void fractions at the tops of any of the cathode half cell chambersin the six-cell electrolyser module.

Example 3

Next, the number of cells in the electrolyser module of Example 2 wasincreased to 200 cells. The fluid flows in the 200-cell electrolysermodule were modeled by CFD. For simplicity, the fluid flows on thehydrogen (cathodes) side only are described herein. The results for eachhalf cell were similar to those obtained for half cells in six-cell and50-cell electrolyser modules, demonstrating the inherent scalability ofthe design. For example, the range of fluid flow rates in the degassedliquid passages in the 200-cell electrolyser module was identical to therange of fluid flow rates in the degassed liquid passages in the 50-cellelectrolyser module. Similarly, void fractions at the tops of the 200cathode half cell chambers were almost equal, and also were almost equalto the void fractions at the tops of the cathode half cell chambers inthe 50-cell electrolyser module.

The present electrolyser modules can be used in the production ofvarious gases, for example chlorine and hydrogen by the electrolysis ofbrine, nitrogen and hydrogen by the electrolysis of ammonia, or oxygenand hydrogen in the case of electrolysis of water. The preferredembodiments of the invention described herein concern the electrolysisof water where the hydrogen-liquid and oxygen-liquid mixtures aregenerated in the respective half cell chambers.

It is contemplated that the electrolyser module of the present inventionbe used for large scale (e.g., MW scale), high pressure applications.

The foregoing description of the preferred embodiments and examples ofthe apparatus and process of the invention have been presented toillustrate the principles of the invention and not to limit theinvention to the particular embodiments illustrated. It is intended thatthe scope of the invention be defined by all of the embodimentsencompassed within the claims and/or their equivalents.

1. An electrolyser module comprising a plurality of structural plateseach having a sidewall extending between opposite end faces with a halfcell chamber opening and at least two degassing chamber openingsextending through said structural plate between said opposite end faces;said structural plates being arranged in face to face juxtapositionbetween opposite end pressure plates; each said half cell chamberopening at least partially housing electrolytic half cell componentscomprising at least an electrode, a bipolar plate in electricalcommunication with said electrode and a membrane, said structural platesand half cell components defining an array of series connectedelectrolytic cells surmounted by at least first and second degassingchambers each having an upper section above a lower section; saidstructural plates defining at least when in said face to facejuxtaposition, respective gas-liquid passages extending between a toppart of the half cell chambers and a bottom part of said upper sectionof said first and second degassing chambers to provide fluidcommunication between an anode part of said electrolytic cells and saidfirst degassing chamber and between a cathode part of said electrolyticcells and said second degassing chamber; said structural plates furtherdefining, at least when in said face to face juxtaposition, respectivediscrete degassed liquid passages extending between a bottom part ofsaid lower section of said first and second degassing chambers and abottom part of said half cell chambers for degassed liquid return fromsaid first and second degassing chambers respectively to said anode andcathode parts of said electrolytic cells; said electrolyser modulefurther comprising respective gas discharge passages fluidlycommunicating with said first and second degassing chambers and at leastone feed water passage extending therethrough and fluidly communicatingwith at least one of said first and second degassing chambers for gasdischarge from said first and second degassing chambers and for feedwater introduction into at least one of said first and second degassingchambers; said electrolyser module further comprising at least oneliquid communication passage for liquid communication between said atleast first and second degassing chambers.
 2. An electrolyser module asclaimed in claim 1 wherein said at least one liquid communicationpassage is defined by at least one surface channel extending into atleast one of the opposite end faces of at least one of said end pressureplates and special structural plates in conjunction with the adjacent ofsaid opposite end faces.
 3. An electrolyser module as claimed in claim 1wherein said at least one liquid communication passage comprisesinternal passages in the body of at least one of said end pressureplates and special structural plates.
 4. An electrolyser module asclaimed in claim 1 wherein said at least one liquid communicationpassage comprises at least one of tube and pipe, in liquid communicationwith said first and second degassing chambers via internal passagescontained in said end pressure plates.
 5. An electrolyser modulecomprising a plurality of structural plates each having a sidewallextending between opposite end faces with a half cell chamber openingand at least two degassing chamber openings extending through saidstructural plate between said opposite end faces; said structural platesbeing arranged in face to face juxtaposition between opposite endpressure plates; each said half cell chamber opening at least partiallyhousing electrolytic half cell components comprising at least anelectrode, a bipolar plate in electrical communication with saidelectrode and a membrane, said structural plates and half cellcomponents defining an array of series connected electrolytic cellssurmounted by at least first and second degassing chambers each havingan upper section above a lower section; said structural plates definingat least when in said face to face juxtaposition, respective gas-liquidpassages extending between a top part of the half cell chambers and abottom part of said upper section of said first and second degassingchambers to provide fluid communication between an anode part of saidelectrolytic cells and said first degassing chamber and between acathode part of said electrolytic cells and said second degassingchamber; said structural plates further defining, at least when in saidface to face juxtaposition, respective discrete degassed liquid passagesextending between a bottom part of said lower section of said first andsecond degassing chambers and a bottom part of said half cell chambersfor degassed liquid return from said first and second degassing chambersrespectively to said anode and cathode parts of said electrolytic cells;said electrolyser module further comprising at least one intermediatepressure plate interspersed between said structural plates along saidlength of said electrolyser module; each said at least one intermediatepressure plate comprising opposite end faces with a sidewall extendingtherebetween, said intermediate pressure plate defining at least one offirst and second degassing chamber openings and through holes extendingbetween its opposite end faces for fluidly communicating respectivelywith said first and second degassing chambers for receiving gastherefrom; said electrolyser module further comprising respective gasdischarge passages fluidly communicating with said first and seconddegassing chambers and at least one feed water passage extendingtherethrough and fluidly communicating with at least one of said firstand second degassing chambers for gas discharge from said first andsecond degassing chambers and for feed water introduction into at leastone of said first and second degassing chambers; said electrolysermodule further comprising at least one liquid communication passage forliquid communication between said at least first and second degassingchambers.
 6. An electrolyser module as claimed in claim 5 wherein saidat least one liquid communication passage is defined by at least onesurface channel extending into at least one of the opposite end faces ofat least one of said end pressure plates, said intermediate pressureplates and said special structural plates in conjunction with theadjacent of said opposite end faces.
 7. An electrolyser module asclaimed in claim 5 wherein said at least one liquid communicationpassage comprises internal passages in the body of at least one of saidend pressure plates, said intermediate pressure plates and said specialstructural plates.
 8. An electrolyser module as claimed in claim 5wherein said at least one liquid communication passage comprises atleast one of tube and pipe, in liquid communication with said first andsecond degassing chambers via internal passages contained in said atleast one intermediate pressure plate.